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[PATCH v5 5/5] perf: powerpc: choose local entry point with kretprobes

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  [PATCH v5 5/5] perf: powerpc: choose local entry point with kretprobes "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> - 2017-03-08 09:30 +0100
    Re: [PATCH v5 5/5] perf: powerpc: choose local entry point with  kretprobes Masami Hiramatsu <mhiramat@kernel.org> - 2017-03-08 11:40 +0100
      Re: [PATCH v5 5/5] perf: powerpc: choose local entry point with  kretprobes "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> - 2017-03-08 12:50 +0100

#1594929 — [PATCH v5 5/5] perf: powerpc: choose local entry point with kretprobes

perf now uses an offset from _text/_stext for kretprobes if the kernel
supports it, rather than the actual function name. As such, let's choose
the LEP for powerpc ABIv2 so as to ensure the probe gets hit. Do it only
if the kernel supports specifying offsets with kretprobes.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
 tools/perf/arch/powerpc/util/sym-handling.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/tools/perf/arch/powerpc/util/sym-handling.c b/tools/perf/arch/powerpc/util/sym-handling.c
index 1030a6e504bb..39dbe512b9fc 100644
--- a/tools/perf/arch/powerpc/util/sym-handling.c
+++ b/tools/perf/arch/powerpc/util/sym-handling.c
@@ -10,6 +10,7 @@
 #include "symbol.h"
 #include "map.h"
 #include "probe-event.h"
+#include "probe-file.h"
 
 #ifdef HAVE_LIBELF_SUPPORT
 bool elf__needs_adjust_symbols(GElf_Ehdr ehdr)
@@ -79,13 +80,18 @@ void arch__fix_tev_from_maps(struct perf_probe_event *pev,
 	 * However, if the user specifies an offset, we fall back to using the
 	 * GEP since all userspace applications (objdump/readelf) show function
 	 * disassembly with offsets from the GEP.
-	 *
-	 * In addition, we shouldn't specify an offset for kretprobes.
 	 */
-	if (pev->point.offset || (!pev->uprobes && pev->point.retprobe) ||
-	    !map || !sym)
+	if (pev->point.offset || !map || !sym)
 		return;
 
+	/* For kretprobes, add an offset only if the kernel supports it */
+	if (!pev->uprobes && pev->point.retprobe) {
+#ifdef HAVE_LIBELF_SUPPORT
+		if (!kretprobe_offset_is_supported())
+#endif
+			return;
+	}
+
 	lep_offset = PPC64_LOCAL_ENTRY_OFFSET(sym->arch_sym);
 
 	if (map->dso->symtab_type == DSO_BINARY_TYPE__KALLSYMS)
-- 
2.11.1

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#1595031 — Re: [PATCH v5 5/5] perf: powerpc: choose local entry point with kretprobes

On Wed,  8 Mar 2017 13:56:10 +0530
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:

> perf now uses an offset from _text/_stext for kretprobes if the kernel
> supports it, rather than the actual function name. As such, let's choose
> the LEP for powerpc ABIv2 so as to ensure the probe gets hit. Do it only
> if the kernel supports specifying offsets with kretprobes.

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>

This patch is OK. And I found that most of functions in sym-handling.c
are used only when libelf is supported. (e.g. probe-event.c itself
is not built when we have no libelf)
So, for the next cleanup, this file should not be compiled without
libelf.

Thanks!

> 
> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> ---
>  tools/perf/arch/powerpc/util/sym-handling.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/arch/powerpc/util/sym-handling.c b/tools/perf/arch/powerpc/util/sym-handling.c
> index 1030a6e504bb..39dbe512b9fc 100644
> --- a/tools/perf/arch/powerpc/util/sym-handling.c
> +++ b/tools/perf/arch/powerpc/util/sym-handling.c
> @@ -10,6 +10,7 @@
>  #include "symbol.h"
>  #include "map.h"
>  #include "probe-event.h"
> +#include "probe-file.h"
>  
>  #ifdef HAVE_LIBELF_SUPPORT
>  bool elf__needs_adjust_symbols(GElf_Ehdr ehdr)
> @@ -79,13 +80,18 @@ void arch__fix_tev_from_maps(struct perf_probe_event *pev,
>  	 * However, if the user specifies an offset, we fall back to using the
>  	 * GEP since all userspace applications (objdump/readelf) show function
>  	 * disassembly with offsets from the GEP.
> -	 *
> -	 * In addition, we shouldn't specify an offset for kretprobes.
>  	 */
> -	if (pev->point.offset || (!pev->uprobes && pev->point.retprobe) ||
> -	    !map || !sym)
> +	if (pev->point.offset || !map || !sym)
>  		return;
>  
> +	/* For kretprobes, add an offset only if the kernel supports it */
> +	if (!pev->uprobes && pev->point.retprobe) {
> +#ifdef HAVE_LIBELF_SUPPORT
> +		if (!kretprobe_offset_is_supported())
> +#endif
> +			return;
> +	}
> +
>  	lep_offset = PPC64_LOCAL_ENTRY_OFFSET(sym->arch_sym);
>  
>  	if (map->dso->symtab_type == DSO_BINARY_TYPE__KALLSYMS)
> -- 
> 2.11.1
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>

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#1595091 — Re: [PATCH v5 5/5] perf: powerpc: choose local entry point with kretprobes

On 2017/03/08 11:31AM, Masami Hiramatsu wrote:
> On Wed,  8 Mar 2017 13:56:10 +0530
> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
> 
> > perf now uses an offset from _text/_stext for kretprobes if the kernel
> > supports it, rather than the actual function name. As such, let's choose
> > the LEP for powerpc ABIv2 so as to ensure the probe gets hit. Do it only
> > if the kernel supports specifying offsets with kretprobes.
> 
> Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
> 
> This patch is OK. And I found that most of functions in sym-handling.c
> are used only when libelf is supported. (e.g. probe-event.c itself
> is not built when we have no libelf)
> So, for the next cleanup, this file should not be compiled without
> libelf.

There are still a few functions there which work without libelf. But, I 
agree that the file has far too many #ifdefs between ABIv2 and libelf. I 
will see if I can simplify this file.

Thanks,
Naveen

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